1. Field of the Invention
The present invention relates to an imaging apparatus and, more particularly, to a focus adjustment method used for the imaging apparatus.
2. Description of the Related Art
Contrast auto-focus (AF) control is a major AF control method used in video cameras or the like. According to the contrast AF control, an AF evaluation value, which represents an in-focus state (contrast state) of an image signal, is generated. The AF evaluation value is generated using an image sensor while a focus lens is moving. Then, a position of the focus lens where the AF evaluation value is largest is searched.
However, in capturing an image of a human figure, due to contrast between a human figure as a main object and its background, in some cases, background objects are focused rather than the human figure.
In order to solve this issue, an imaging apparatus having a face detection function has been developed. Japanese Patent Application Laid-Open No. 2006-227080 discusses an imaging apparatus that sets a focus detection area corresponding to a recognized face area and performs focus detection.
Further, Japanese Patent Application Laid-Open No. 2001-215403 discusses an imaging apparatus that detects an eye of a human figure, sets a focus detection area corresponding to the area of the eye, and performs focus detection.
Further, Japanese Patent Application Laid-Open No. 2004-212556 discusses an imaging apparatus, which expands the focus detection area when determining focus if a movement of an object is detected during imaging or if a camera movement such as panning or tilting (hereinafter simply referred to as “panning”) is detected.
However, in using a camera with live view function that can capture a moving image, different from the case of capturing a still image, the object tends to keep moving. Thus, it is difficult to recognize a face with stability and thus the AF control becomes unstable.
If a face is recognized, then, by specifying a face area as the area to be focused, the in-focus state of the human figure can be stabilized. However, if the person turns his face away or closes his eyes, or if camera shake occurs, then the face recognition becomes difficult.
Under such an imaging condition where the recognition of the face varies depending on the condition of the object, if an area used for detecting focus is changed depending on whether the face is recognized or not, the AF evaluation value will be affected, and stable focus adjustment cannot be achieved.
Further, various objects come in and out of the screen area when a moving image is captured. A user generally captures a moving image by arranging the object position at the center of the screen. However, if a face of another person is recognized, and if the face is focused, then the object will not be in-focus as intended by the user.
Furthermore, sometimes it is difficult to detect a face depending on a movement of the object, a change in camera angle, or a camera work such as panning. In such a case, even if the focus area is expanded in determining focus when a camera movement is detected as discussed in Japanese Patent Application Laid-Open No. 2004-212556, it is difficult to follow the movement of the main object. Thus, the AF evaluation value of the moving image obtained from such a focus detection area becomes unstable.